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We demonstrate the formation of metal alloys in Au-Ag, Au-Cu and Au-Pd systems and the experimental determination of their optical properties using optical transmission and reflection spectroscopy. The optical constants define the plasmon resonance wavelength and electromagnetic field local intensity. However, the optical constants behavior cannot be precisely modeled based on the data of pure metals due to unknown morphology and composition of the alloy. It has to be determined experimentally. We demonstrate the surface-enhanced Raman scattering using alloy metals. Depending on the metal to which molecules are adsorbed, we observe enhancement of different Raman modes. It is mainly due to the chemical enhancement effect between metal and molecules. [ABSTRACT FROM AUTHOR]

An intricate relationship is revealed between the intensity of surface‐enhanced Raman scattering (SERS) and the optical extinction. The unusual trends of SERS intensity decrease while the extinction increases observed in experiments is fully explained for the first time. The SERS intensity is well known to be strongly correlated with the extinction at excitation and Stokes wavelengths, but the dependence is more involved than the simple product of the two extinction enhancements. The radiative and nonradiative losses, different for different Stokes wavelengths, strongly affect the relationship between SERS and extinction. Dye molecules are shown experimentally and numerically to experience different local field enhancements for the different Raman modes, and a simple qualitative analytical description of this universal phenomenon is provided here. [ABSTRACT FROM AUTHOR]

Plasmonic photocatalysis, i.e., photocatalysis with activity under visible-light (vis) irradiation due to plasmonic feature of noble metals (NMs), has been intensively studied as promising method for solar energy conversion. Although various plasmonic photocatalysts have already been investigated, the vis activity is usually low, and thus should be improved for commercial application. Moreover, considering charge carriers' mechanism, the stability of NMs during long-term irradiation should be also considered. Accordingly, this study has focused on the improvement of photocatalytic activity and stability of gold-modified titania photocatalysts under vis irradiation. Among a few proposed synthesis procedures, modified photodeposition method has resulted in the formation of TiO 2 /Au/TiO 2 composites with high level of photoactivity. Large gold nanoparticles (NPs), formed on large rutile titania particles, are partially covered with fine anatase titania NPs, and thus the interface between titania and gold has been enlarged. Moreover, partial coverage of gold by fine titania NPs hinders gold aggregation, resulting in improved stability of these samples. Action spectrum of 2-propanol oxidation and numerical 3D-FDTD simulations of field distribution have indicated that the enhanced utilization of incident photons is responsible for high activity of TiO 2 /Au/TiO 2 photocatalysts. [Display omitted] • Long-term vis-irradiation causing gold aggregation and loss from the reaction system. • Photocatalyst suspension stirring even in the dark results in gold coalescence. • Enhanced photocatalyst performance by improved interface between gold and titania. [ABSTRACT FROM AUTHOR]